Material level indicator

ABSTRACT

A material level indicator of the drop or bob weight type comprising a housing having a central partition flanked by two covers defining separated chambers into which the electrical and mechanical components respectively are positioned. The indicator also incorporates improvements in sealing of the housing during both off-cycle and on-cycle conditions, maintenance and adjustment features, and pulse generating apparatus and circuitry.

Unlted States Patent 1191 1111 3,838,518

Hendrickson I Oct. 1, 1974 MATERIAL LEVEL INDICATOR 3,686,507 8/1972 Krutz et a]. 324/168 3,727,033 4/1973 Bassist 324/171 [75] Inventor' zz Hendmkson, Hum, 3,781,624 12/1973 T111115 33/I26.6 x

10 FOREIGN PATENTS OR APPLICATIONS [73] Asslgnee' gg kf Company Part Huron I,289,09I 2/1962 France 33/1266 Filed: 1 1973 Primary ExaminerLouis R. Prince [21] APPL NOJ 323,979 Assistant Examiner-Charles E. Phillips Attorney, Agent, or FirmBarnes, Kisselle, Raisch & Choate [52] US. Cl. 33/l26.6, 324/171 [51] Int. Cl. GOlf 23/00 581 Field Of Search 33/1266; 73/321; 324/168, [57] ABSTRACT 324/171 A material level indicator of the drop or bob weight type comprising a housing having a central partition [56] References Ci d flanked by two covers defining separated chambers UNITED STATES PATENTS into which the electrical and mechanical components 6 respectively are positioned. The indicator also incor- 11 porates improvements in sealing of the housing during 2854752 10/1958 z f "33/1266 both off-cycle and on-cycle conditions, maintenance 2:869:239 1 1959 .Iurs et 111:3: :1: 33/1266 and adjustment features and Pulse generating appara- 3,036,460 5/1962 White 61 a1. 324/168 and Circuitry- Lanham i. 33/l26.6 X 18 Claims 16 Drawing Figures Mayer et a] 33/I26.6 x

PATENTED 7 1974 MATERIAL LEVEL INDICATOR This invention relates to material level indicators.

In gauging the level of materials, such as granular materials stored in bins, it has heretofore been suggested that a bob weight or the like be utilized at the end of the cable and be lowered so that when it engages the material, the tension on the cable is relieved, indicating that the level has been determined. The length of cable extended or fed upon such engagement with the material is a measure of the level of the material in the container or bin.

Among the objects of the invention are to provide an improved material level indicator of the aforementioned type which is relatively simple inconstruction. durable, utilizes a minimum number of components. and which requires minimum maintenance yet may be readily serviced.

Other objects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a fragmentary partly diagrammatic perspective view of an exemplary but preferred embodiment of a material level indicator of the invention.

FIG. 2 is a fragmentary side elevational view of the same.

FIG. 3 is a front elevational view of the same with the front cover removed.

FIG. 4 is a fragmentary rear elevational view of the same with the rear cover broken away.

FIG. 5 is a sectional view taken along the line 55 in FIG. 3.

FIG. 6 is a fragmentary exploded perspective view of a counter signal generating portion of the indicator.

FIG. 7 is a fragmentary exploded perspective viewof a cable tension sensing switch arrangement of the indicator.

FIGS. 8 and 9 are fragmentary part center sectional views on an enlarged scale of a bob weight seal and shut-off mechanism employed in the indicator shown in FIG. 5 showing the parts in different operative positions.

FIG. 10 is a sectional view through one embodiment of a bob weight portion of the indicator.

FIG. 11 is a diagrammatic view showing the manner in which the lower end of the cable is secured by a spool-in the bob weight of FIG. 10.

FIG. 12 is a schematic wiring diagram of the control and indicating circuit employed in the indicator.

FIG. 13 is an enlarged sectional view of the idler counter pulley mechanism of the indicator.

FIGS. 14 and 15 are views similar to FIGS. 8 and 9 of a second form of bob weight seal and shut-off mechanism of the indicator.

FIG. 16 is a sectional view similar'to FIGS. 8 and 9 and 14 and 15 showing a third form of bob weight seal and shut-off mechanism of the indicator.

Referring in moredetail to the accompanying drawings, FIG. 1 illustrates an indicator 10 embodying the invention which is adapted to be mounted on the top 11 of a bin or similar container for gauging the height of the material M in the container. The indicator 10 comprises a sealed housing 12 which includes a central portion or wall 13, which may be an aluminum casting or the like, and front and rear covers 14 and 15 mounted on opposite sides of the central portion 13' and cooperating therewith to define a front chamber 16 for the mechanical components (FIGS. 3 and 5) and a rear chamber 17 for the electrical components (FIGS. 4 and 5).

A cable supply drum or pulley 18 (FIGS. 3 and 5) is rotatably mounted on a shaft 19 journalled by a bushing 20 in an opening in the central portion 13. The cable C fed from pulley 18 is trained over a pulley 21 that has a peripheral V groove 22 therein (FIG. 13) and thereafter passes over a level sensing pulley 23 journalled by a stub shaft 23 on the end of a level sensing lever 24. Lever 24 is rotatably mounted by means of a tube 25 in an opening 26 (FIG. 7) in portion 13. A torsion spring 27 having a central loop 28 and end portions 29, 30 is mounted on the tube 25 with loop 28 encircling the tube and the free end 31 of the portion 29 engaging the level sensing lever 24 to yieldingly urge it upwardly. The free end 32 of the other end portion 30 engages one of a series of serrations or teeth 33 on a sector forming a part of the central portion 13. The tension on the sensing lever 24 can be adjusted by rotating the spring 27 with respect to the central portion 13 and bringing the free end 32 selectively into position with different serrations. If desired. as a safety measure clamp 34 held in position by a screw 35 may be used to'hold the portion 30 in any selected position.

The chamber 16 is vertically separated into two portions by a wall 36 (FIGS. 3 and 5) and the cable passes downwardly from the upper chamber portion 160 through an apertured wiper button 37, made from thermoplastic material such as Delrin (trademark), mounted in wall 36 into the lower chamber portion 16b and thereafter downwardly and outwardly of the housing through a standpipe pedestal D into the container. A sensing drop weight or bob weight is fastened to the free end of the cable C as described in more detail hereinafter.

' The electrical components in rear chamber 17 comprise an electrical motor 40 (FIGS. 4 and 5), preferably which includes a reduction gearing 41 for rotating the cable drum 18 through the shaft 19. A rotary cam 42 is fixed to the end of tube 25 opposite the end on which lever 24 is fixed and upon oscillation of lever 24 cam 42 operates a two-position switch 43 via its cam follower switch arm 43'. A rotary disc 44 (FIGS. 4and 6) is'fixed to the end of a shaft 45 opposite that on which pulley 21 is fixed to rotatably drive shaft 45..Disc 44 is provided with a plurality of longitudinally polarized bar magnets 46 individually mounted in equally spaced grooves 47 therein and extending tangentially from the periphery of spacer hub 48. The magnets 46 are adapted to move past a hermetically sealed reed switch 49 mounted in a groove 50 of a plastic plate 51 which, in turn, is loosely spindled via hole 51' on shaft 45 and supported by screws 51a on cover 15 for limited adjustment; i.e., plate 51 can be pivoted on the mounting screw 51d received in hole 51c due to the clearance provided in the keyhole slots 51b. Switch 49 is thus positioned closely adjacent the path of travel of magnets 46 and is oriented offset radially from the axis of rotation of disc 44 such that the longitudinal axis of switch 49 is parallel to and coterminous with the axis of each magnet as the same sweeps by the switch. Partition l2 is'provided with a recess 13c to accommodate switch 49 and its associated leads. A second cam 53 is fixed on the end of shaft 54 opposite that to which a shut-off switch operating lever 55 is fixed.

In operation, as described in more detail hereinafter, to initiate a material level sensing cycle motor 40 is energized in the properdirection to pay out cable C permitting the bob weight B to move downwardly from its fully raised position, allowing lever 55 to pivot clockwise to its on position shown in FIG. 3. When weight B engages the material M, the tension on the cable is relieved so that the spring 27 can rotate lever 24 clockwise as viewed in FIG. 3 to its up position, thus rotating cam 42 to operate the switch 43 to thereby apply reversing current to motor 40 so that it rotates in the opposite direction. This causes the cable to be wound onto drum 18 while again depressing lever 24. As weight B returns to its uppermost position, lever 55 is lifted so as to pivot in a counterclockwise direction to its off position (FIG. 9), thereby rotating cam 53 to actuate a switch 56 via its cam follower arm 56 and thereby stop the operation of motor 40.

Referring to FIGS. and 11, in one embodiment of the invention cable C is fastened to weight B preferably by an arrangement which includes a spool 60 having an axial groove 61 and helical groove 62 therein. The cable C is first passed downwardly through a central through bore 63 in weight B and then, with spool 60 detached from weight B, the cable is shipped sideways into groove 61 and then wound around the helical groove 62 with its free end C laid short of the upper end of groove 62. The spool 60 is then inserted upper end first into an eccentric'recess 64 in weight B and held therein by a screw 65 inserted upwardly through the center bore 60 of spool 60. The close fit of the cable wound spool in its recess thus traps the cable in the helical groove 62, thereby obviating the need to knot or otherwise secure the cable while allowing some latitude for adjustment of the effective cable length.

One form of bob weight seal for actuating the motor shut-off lever 55 is shown in FIGS. 8 and 9 and comprises a plastic tube 66 which has a flexible washer 67 fixed thereto spaced below a flange 68 at the upper end of the tube between which the bifurcated end 69 of the lever 55 extends. A tubular resilient plastic bellows 70 yieldingly urges tube 66 downwardly. Bellows 70 comprises longitudinally spaced corrugations 71 and a cylindrical upper end adhesively secured and sealed in a counterbore 13a in housing portion 13. The lower end of bellows 70 has an inturned flange secured to a flange 72 on tube 66. A resilient gasket 73 on the lower end of the flange 72 is adapted to engage a conical portion 73' of weight B to provide a seal between the interen- 'gaging surfaces. As the cable C is raised, weight B engages the lower end of tube 66 via gasket 73, thereby forcing the tube upwardly and, in turn, pivoting lever 55 upwardly to rotate the cam 53 to thus actuate switch 56 to shut off motor 40. During this time, the cable is passing upwardly with a close sliding fit through the wiper button 37 before it is wound onto the drum 18, thereby preventing foreign materials from passing upwardly beyond chamber 16b. The chamber 16b in conjunction with wiper 37 thus helps isolate the principal mechanical components from contamination by foreign material while the weight is disengaged from seal 6673. During the off cycle, such isolation is accomplished by the weight B engaging gasket 73. As best seen in FIG. 5, cover 14 has a pocket 140 which is aligned with and forms part of chamber 1612, but which extends below a lower downwardly and outwardly sloping wall 13b of housing 13 so that most or all of the dirt or other foreign material scraped loose from cable C by wiper 37 will tend to slide off wall 13b and collect in the lower portion of pocket 14a. Hence, when cover 14 is removed for servicing of the unit, the accumulated foreign material will fall downwardly out of pocket 140 clear of the unit.

In the form of the weight seal and shut-off mechanism of the invention shown in FIGS. 14 and 15, a rigid tube 75 has a washer seal 76 encircling and secured to its outer periphery near the upper end of the tube and adapted to engage wall 131) to seal the housing bore 130 in the lowermost position of tube 75. The lower end of tube 75 is secured to a flat resilient diaphragm 77 having a cup-shaped flange 78 seated in the counterbore recess 13a in the lower end of the housing. The central portion of the diaphragm 77 is thickened and formed with a frustoconical depression 80 into which the upper end of the bob weight B nests as it is raised. Surrounding this thickened portion 80 are annular slits 81 which define annular portions 81 that seal against the conical surface 73' of weight B when it is elevated to lift tube 75 and thereby raise lever 55 to its shut-off position of the tube. However. the forks of lever 55 rest on a 4 flanged wiper button 75a inserted in and fixed to the upper end of tube 75 through which cable C passes with a sliding fit. Hence, as with tube66, some of the foreign material clinging to cable C will be wiped therefrom as the cable passes upwardly through the tube and will fall downwardly via the hollow tube back into the storage bin while the weight is ascending toward engagement with the shut-off seal. Final wiping, with a closer sliding fit, is nevertheless still performed by wiper 37, in order to avoid false actuation of lever 55 due to premature lifting of tube 66 or 75 which might be caused by too severe a wipingaction in the tube.

In the third form of weight seal and shut-off mechanism of the invention shown in'FIG. 16, a rod 85 is threadably fixed on the upper end of weight B and has a blind bore in its upper end into which the lower end of cable C is inserted and secured by crimping of rod 85. The upper end of rod 85 forms a shoulder 86 for actuating the bufurcated end of lever 55. In this embodiment, the seal is in the form of a cup-shaped resilient diaphragm 87 having a flat disc 88 with a cylindrical flange 89 secured within the recess 13a and a central opening 91 through which the rigid member 85 extends. As in the previous form of the invention, when the cable is raised, weight B engages the diaphragm 87 to flex the disc portion 87 upwardly, conforming it in sealed relation to the weight surface 73 while permitting continued upward movement of the weight so that shoulder 86 can engage lever 55, thereby actuating the associated cam to stop the motor.

Whenever cable C is being paid out or pulled in, magnet carrier disc 44 is caused to rotate to generate via reed switch 49 a continuous series of pulse signals which are indicative of the amount of cable being paid out or drawn in. These signals produced by actuation of reed switch 49' maybe transmitted to a counter and,

in turn, to a readout device which is calibrated in accordance with the number of pulse signals produced to provide a reading that corresponds to the depth of the material being gauged.

The control and indicating circuit employed in indicator 10 is'shown in the schematic circuit diagram of FIG. 12 wherein all switches and relay contacts are shown in their normal position with power off and the sensing weight B in its fully raised position. Under this condition, all contacts labelled NC closed) will be in their closed condition. and all contacts labelled NO" (normally open) will be in their open condition. To start a cycle of operation of indicator 10, the manual start switch 100 is depressed to close a power circuit to motor 40 via power lead 102, fuse 104, contacts 106, lead 108, the windings of motor 40, lead 110, the normally closed contacts of reversing switch 112, lead 114, lead 116 and the other power-ten minal lead 118. Depressing switch 100 will also close reset contacts 107 which resets the counter 130 to an appropriate starting value. Motor 40 is thus energized to rotate in the proper direction, to unwind cable C from drum 18 tothereby lower the sensingweight B. As soon as the weight has dropped the short distance required to allow lever 55 to actuate switch 56 from its normally closed to its normally open position, manual switch 100 can be released since a power connection,

now exists to motor 40. via lead 102, fuse 104, lead 120,

(normally lead 122, the now closed. NO contact of switch 56 and lead 124. Thus, the motor will continue to run tolower the weight B until it contacts the material M stored in the bin.

During the descent of weight B, the cable passing around pulley 21 will rotate the magnet carrier disc 44. As each of the magnets 46rsweepby the reed switch 49, the magnetic field emanating from the magnet will first cause the reeds of switch 49 to close and then reopen as the magnet moves away from the reed switch, Assuming that a readout is desired during descent of weight B, upon closure of the contactsof switch 49, current from lead 102 is supplied to the conventional pulse counter l30.via lead 132, the NC contacts of a single pole-double-throw relay l34, the armof a selector switch 135, lead 136 and lead .l 38;con nected tothe pulse signal input terminal of counter 130, Thus, counter 130 will, with selector switch 135 so positioned, provide-a readout of the amount of cable paid out.

As weight B comes to rest on the materials M andthe drum 18 continues unreeling the cable, the force exerted by the cable on pulley 23 will decrease, allowing spring 27 to bias lever 24 upwardly clockwise as viewed in FIG. 3 and thereby operate the level sensing switch 43 so that its contact arm movesfrom the NC position.

to the NO position. This completes an energizing path for a relay coil 140 via lead 142, lead 144, lead 146 and lead 116. When the coil 140 isthus energized, the condition of three sets of associated contacts are simultaneously changed.

Energizing relay coil 140 shifts the switch arm of the reversing relay contacts 112 to make contact with the NO contact, thereby opening lead. 110 and closing a connection to the motor vialead 148 so that reversing current is now applied to the motor so that it now rotates drum 18 in the reverse direction to wind up the cable on the drum.

Energizing relay 140 also causes the switch arm of relay contacts 134 to move from the NC'to the NO contact, thereby providing a parallel power path via.

which in turn-causes the lever arm 24 tobe pulled down against the bias of spring 27 to the position shown in FIG. 3. 1 i

The actuation of contacts 134 by the energization of relay 130 also opens up the power connection, through the reed switch 49 via lead 132. Hence, reverse rotation of the magnet carrier disc 44 in response to the cable being reeled up, although continuing to, actuate the switch 49, will not generate any further counter pulses tobe applied to counter 130 unless an alternative power path is provided across the contacts. of the reed switch 49. Such a power path may be provided by means of a lead 152 connected at one end through. lead 120 to the power lead 102 and connected at its other end to the center tap of a set of contacts 154 controlled by relay coil 140. Hence, when relay coil 1 4,0. is,ener gized, the switch arm of contacts 154 willg move from the NO position to the NC position to connectlead. 152 to lead 136 via selector switch 135, provided the same has been switched to the phantom position shown in FIG. 12 to make contact with the NC terminal of contacts 154. Hence, in this mode pulse signals will be applied to counter 130 in response to. closure of the contacts of reed switch 49-as the weight B is raised. Thus, counter 130 will nowprovide a readout of the "amount of cable reeled in.

When weight B reaches the upper limit of its travel, lever 55 will be pivoted upwardly counterclockwise, as described previously, at the same time-weight B ismaking a sealing engagement with the diaphragm of seals 70, 77 or 87 described previously. Thus, shut-off switch 56 will be-actuated to return to its NC position, thereby disconnecting power from motor 40 to shut it offiwhile also-opening the circuit via lead 132 to the holding-in NO contacts 134, thereby de-energizir g relaycoil 140. This causes the three sets of associated relayv contacts 112, 134 and 154 to return to their respective; conditions shown in FIG. 12, thus finishing one complete cycle and conditioning the circuit for the initiation of the next cycle.

The reading on the output dial of the digital counter at the completion of a cycle will thus provide an indication of the distance from the indicator 1.0 to the top of the material contained in the storageunit. when switch 135 is set to count the amount of cable paid out, counter 130 will hold whatever reading has been generated during the descent of the weight while the weight is, being raised back up to its starting position. If contacts 154 are used. the pulsesare generated only during ascent of weight B, and hence the counter will operate only during ascent so that at the end of the cycle it will provide a reading corresponding to the amount of cable reeled in.

Normally the portion of the circuitry and controls indicated within the broken line block shown inFIG. 12 are contained within the housing ofindicator 10, whereas the circuit components indicated inthe broken line block 162 are normally mounted remote from ventiondeach of the three shafts 19, 45 ands-4 which extend through the otherwise imperforatewall of the central portion 13 of the housing have a flexible cupor lipseal mounted in a counterbore opening toward front chamber 16. The lip seal 170 associated with shaft 45 and its bushing 45' is best seen in FIG. 13

wherein seal 170 is shown arranged with its flexible frustoconical central portion 172 converging toward the front chamber 16, shaft 45 having a sealed rotating fit therein. With this arrangement, the only through openings extending between chamber 16 and rear chamber 17 are securely sealed against dirt and dust which may enter chamber 16 from the storage container through the cable passageway when weight B is disengaged from the shut-off seal mechanism. Seals 170 are also priented so that they respond to an increase in pressure in chambers 16 or 16b so as to flex in a direction to increase the sealing pressure exerted by the seal on its associated shaft. Hence, they will tend to prevent dust or dirt from being blown from the front chambers 16a and 16b toward the rear chamber 17 whenever a pressure differential is created therebetween. Such a condition may occur when the bin or vessel is subjected to pressure changes, and it does occur when weight B is being lifted after its initial engagement with the shut-off seal (FIG. 14) to its fully raised position (FIG. 15) due to the resultant decrease in volume of chamber 16. Hence, the electrical components of the indicator 10 are maintained by themselves in a well-protected rear chamber 17 which is isolated from dust, dirt or other foreign material by both the imperforate partition 13 and dual chambers 16a and 16b and associated seals of the front chamber.

, From the foregoing description, it will now be apparent that a material level indicator constructed in accordance with and embodying the features of the present invention provides a unit which is rugged in construction and reliable in operation even under adverse environmental conditions. The unit may be readily serviced in situ by removal of the front cover 14 for access to the mechanical components and/or removal of the rear cover 15 for access to the electrical components. The weight and seal shut-off structure maintains the unit in sealed condition during its off-duty cycle, which ordinarily predominates. During a material sounding cycle, the progressive isolation offered by compartment 16b and wiper 37 helps forestall upward migration of dirt or foreign material into compartment 16a. Moreover, the front cover 14 can be removed and the dust readily cleaned from the front compartments 16a and 16b without any danger of contaminating the electrical components in the rear compartment 17. Likewise, if only electrical servicing is required, cover 15 can be removed while leaving cover 14 on the unit without any danger of having accumulated dirt contaminate the electrical components and also without venting the container to atmosphere via the indicating unit. The isolation of electrical components in a separate chamber 17 also contributes to the explosion-proof character of indicator 10.

The arrangement of the magnet carrier disc 44 and the reed switch 50in stacked relationship in the electrical compartment also facilitates adjustment, removal and servicing of these components when necessary. The particular orientation of reed switch 49 relative to the pin wheel array of magnets 46 on disc 44 maximizes the effect of themagnetic field emanating from the magnets and shortens the duration of the effect of the field to produce clear sharp pulse signals, thereby enhancing the read-out reliability of the pulse counter 130 and making it easier to filter out interference and transient signals. The arrangement of the biasing spring 27 associated with the material sensing lever 24 provides a ready means of adjusting for manufacturing var iations in the springs to give the proper tension on the sensing arm. Similarly the attachment of the cable C to the weight B in the embodiments of H05. 10 and 11 provides a simple means of securing and adjusting the cable in the field.

I claim: j

1.,ln a material level indicator of the drop-weight type, the combination comprising a housing having a central portion, a first cover associated with one side of said central portion and defining therewith upper and lower vertically aligned front chambers in which mechanical components are positioned, a second cover associated with the opposite side of said central portion to define a rear chamber in which electrical components are positioned, said central portion serving as a .sealed'barrier between said rear and front chambers,

said mechanical components disposed in said upper chamber comprising a drum rotatably mounted on said .central portion and having one end of a drop line attached thereto a counter pulley journalled on said central portion, and a level sensing lever pivoted on said central portion and rotatably supporting a level sensing pulley thereon, said drop line being trained over said pulleys and having a bob weight attached to its other end, said upper and lower front chambers having open- .ings through which said drop line extends downwardly therefrom, a shut off switch operating lever pivoted to said central portion in said lower chamber and actuator means adapted to be engaged by said bob weight on said drop line to actuate said operating lever, said electric components comprising an electrical motor for drivingv said drum, a level sensing switch operatively connected with the level sensing lever and a shut off switch operatively connected with said shut-off lever.

increase their sealing engagement with the associated shafts in response to an increase in pressure in said front chambers relative to said rear chamber.

5. The combination set forth in claim 4 wherein said actuator means comprises a tube with said drop line passing therethrough, and diaphragm means supporting said tube in the lower end of said housing such that the upper end of said tube projects into said lower chamher, said tube being liftedupon engagement by the bob weight during upward movement thereof to actuate said shut-off switch. sensing lever.

6. The combination set forth in claim 5 wherein said diaphragm means comprises a tubular longitudinally corrugated resilientbellows having the upper end athereof fixed to said-housing and the other end thereof extending downwardly and surrounding said tube and being secured thereto whereby upon said tube being lifted by said bob weight said bellows is yieldably col- 7. The combination set forth in claim wherein said diaphragm means comprises a generally horizontally extending member having a center aperture with said drop line passing therethrough and annular serrations thereon which are adapted to be engaged by the upper end of said weight and to stretch thereagainst during lifting of said tube by said weight.

8. The combination set forth in claim 4 wherein said actuator means comprises a means interconnecting said weight with said drop line and having an enlargement member fixed thereon spaced above said weight, a diaphragm mounted on said housing and having an aperture through which said drop line extends whereby when the upper end of said weight engages said diaphragm said weight causes said diaphragm to flex, said member having means thereon for engaging said shut off switch actuating lever and said interconnecting means having a predetermined length such that said member moves said lever from an on to an off position during yielding movement of said diaphragm while engaged by said weight.

9. The combination set forth in claim 1 including a rotary magnet carrier in said rear chamber, said magnet carrier being operatively connected to said first pulley, a plurality of magnets mounted on said carrier, said magnets extending longitudinally generally tangentially to a circle concentric with and spaced radially outwardly of the center of rotation of said carrier, and a reed switch mounted on said housing in fixed position such that as said carrier rotates each magnet is brought into generally parallel relation to the reed switch to produce a counting signal.

10. The combination set forth in claim 9 wherein said magnets each comprise longitudinally polarized bar magnets and said reed switch is oriented with its longitudinal axis parallel to the polar axis of each magnet when it sweeps by said reed switch.

11. The combination set forth in claim 10 including means for mounting said rotary switch comprising a plate mounted on said central portion, said plate having said reed switch adhered thereto.

12. The combination set forth in claim 1 including means for yieldingly urging said level sensing lever in one direction comprising a torsion spring, means for adjusting the tension of said torsion spring on said lever comprising a plurality of serrations on said housing.

13. The combination set forth in claim 12 wherein said torsion spring comprises at least one winding with arms extending from the opposite ends of said winding, one of said arms of said torsion spring engaging said level sensing lever, the other of said arms of said torsion spring engaging said serrations.

14. The combination set forth in claim 13 wherein said serrations extend in a curved row having a radius of curvature concentric with said spring winding, and wherein said other arm is curved to conform with the curvature of said row of serrations.

15. The combination set forth in claim 1 including a spool having a helical groove therein and connecting said drop line to said weight, said drop line being wound around said helical groove, said weight having a recess into which said spool extends with the drop line wound thereabout.

16. The combination set forth in claim 15 wherein said spool includes an axial groove in the outer periphery thereof into which said drop line extends prior to being wound about said spool whereby the turns of said drop line wound in said helical groove overlie the portion of said drop line extending in said axial groove.

17. The combination set forth in claim 1 wherein said first cover has a pocket therein juxtaposed with said lower front chamber of said housing and defining a portion thereof, said lower chamber having a bottom wall sloping downwardly toward said pocket, the lowermost portion of said pocket being disposed below said wall whereby dirt or other foreign material collecting in said lower chamber tends to migrate to and deposit in said pocket.

18. The combination set forth in claim 8 wherein upper end of said weight engages said diaphragm to seal said aperture during yielding movement of said diaphragm.

Q UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,838,518

DATED October 1, 1974 b O 3 Paul G. Hendrickson it is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

a Column 2, line 64 "12" should be -l3- Column 7, line 10 "priented" should be -t-oriented- Column 8, lines 31/32 "electric" should be -electricalline 32 "electrical" should be -electric- Column 10, line 38 after "wherein" insert an- Signed and Scaled this 9 Fourteenth D y of March 1978 [SEAL] Attest:

RUTH C. MASON LUTRELLE F. PARKER Attesting Officer Acting Commissioner of Patents and Trademarks 

1. In a material level indicator of the drop-weight type, the combination comprising a housing having a central portion, a first cover associated with one side of said central portion and defining therewith upper and lower vertically aligned front chambers in which mechanical components are positioned, a second cover associated with the opposite side of said central portion to define a rear chamber in which electrical components are positioned, said central portion serving as a sealed barrier between said rear and front chambers, said mechanical components disposed in said upper chamber comprising a drum rotatably mounted on said central portion and having one end of a drop line attached thereto a counter pulley journalled on said central portion, and a level sensing lever pivoted on said central portion and rotatably supporting a level sensing pulley thereon, said drop line being trained over said pulleys and having a bob weight attached to it''s other end, said upper and lower front chambers having openings through which said drop line extends downwardly therefrom, a shut off switch operating lever pivoted to said central portion in said lower chamber and actuator means adapted to be engaged by said bob weight on said drop line to actuate said operating lever, said electric components comprising an electrical motor for driving said drum, a level sensing switch operatively connected with the level sensing lever and a shut-off switch operatively connected with said shut-off lever.
 2. The combination set forth in claim 1 wherein said housing includes a wiping device positioned such that the drop line passes therethrough in traveling between said upper and lower front chambers.
 3. The combination set forth in claim 2 including means operatively connecting said switchEs to the corresponding mechanical components comprises shafts extending through said central portion, and seals provided around said shafts.
 4. The combination set forth in claim 3 wherein said seals comprise pressure responsive lip seals oriented to increase their sealing engagement with the associated shafts in response to an increase in pressure in said front chambers relative to said rear chamber.
 5. The combination set forth in claim 4 wherein said actuator means comprises a tube with said drop line passing therethrough, and diaphragm means supporting said tube in the lower end of said housing such that the upper end of said tube projects into said lower chamber, said tube being lifted upon engagement by the bob weight during upward movement thereof to actuate said shut-off switch sensing lever.
 6. The combination set forth in claim 5 wherein said diaphragm means comprises a tubular longitudinally corrugated resilient bellows having the upper end thereof fixed to said housing and the other end thereof extending downwardly and surrounding said tube and being secured thereto whereby upon said tube being lifted by said bob weight said bellows is yieldably collapsed to cause the tube to actuate said shut-off switch sensing lever.
 7. The combination set forth in claim 5 wherein said diaphragm means comprises a generally horizontally extending member having a center aperture with said drop line passing therethrough and annular serrations thereon which are adapted to be engaged by the upper end of said weight and to stretch thereagainst during lifting of said tube by said weight.
 8. The combination set forth in claim 4 wherein said actuator means comprises a means interconnecting said weight with said drop line and having an enlargement member fixed thereon spaced above said weight, a diaphragm mounted on said housing and having an aperture through which said drop line extends whereby when the upper end of said weight engages said diaphragm said weight causes said diaphragm to flex, said member having means thereon for engaging said shut-off switch actuating lever and said interconnecting means having a predetermined length such that said member moves said lever from an on to an off position during yielding movement of said diaphragm while engaged by said weight.
 9. The combination set forth in claim 1 including a rotary magnet carrier in said rear chamber, said magnet carrier being operatively connected to said first pulley, a plurality of magnets mounted on said carrier, said magnets extending longitudinally generally tangentially to a circle concentric with and spaced radially outwardly of the center of rotation of said carrier, and a reed switch mounted on said housing in fixed position such that as said carrier rotates each magnet is brought into generally parallel relation to the reed switch to produce a counting signal.
 10. The combination set forth in claim 9 wherein said magnets each comprise longitudinally polarized bar magnets and said reed switch is oriented with its longitudinal axis parallel to the polar axis of each magnet when it sweeps by said reed switch.
 11. The combination set forth in claim 10 including means for mounting said rotary switch comprising a plate mounted on said central portion, said plate having said reed switch adhered thereto.
 12. The combination set forth in claim 1 including means for yieldingly urging said level sensing lever in one direction comprising a torsion spring, means for adjusting the tension of said torsion spring on said lever comprising a plurality of serrations on said housing.
 13. The combination set forth in claim 12 wherein said torsion spring comprises at least one winding with arms extending from the opposite ends of said winding, one of said arms of said torsion spring engaging said level sensing lever, the other of said arms of said torsion spring engaging said serrations.
 14. The combination set forth in claim 13 wherein said serrations extend in a curved row having a radius Of curvature concentric with said spring winding, and wherein said other arm is curved to conform with the curvature of said row of serrations.
 15. The combination set forth in claim 1 including a spool having a helical groove therein and connecting said drop line to said weight, said drop line being wound around said helical groove, said weight having a recess into which said spool extends with the drop line wound thereabout.
 16. The combination set forth in claim 15 wherein said spool includes an axial groove in the outer periphery thereof into which said drop line extends prior to being wound about said spool whereby the turns of said drop line wound in said helical groove overlie the portion of said drop line extending in said axial groove.
 17. The combination set forth in claim 1 wherein said first cover has a pocket therein juxtaposed with said lower front chamber of said housing and defining a portion thereof, said lower chamber having a bottom wall sloping downwardly toward said pocket, the lowermost portion of said pocket being disposed below said wall whereby dirt or other foreign material collecting in said lower chamber tends to migrate to and deposit in said pocket.
 18. The combination set forth in claim 8 wherein upper end of said weight engages said diaphragm to seal said aperture during yielding movement of said diaphragm. 